Radius of a conductor increases uniformly from left end to right end as shown in fig.Material of the conductor is isotropic and its curved surface is thermally isolated from surrounding. Its ends are maintained at temperatures $T_1$ and $T_2$ ($T_1$ > $T_2$): If, in steady state, heat flow rate is equal to $H$ , then which of the following graphs is correct

Ice starts forming in lake with water at ${0^o}C$ and when the atmospheric temperature is $ - {10^o}C$. If the time taken for $1 \;cm$ of ice be $7$ hours, then the time taken for the thickness of ice to change from $1\; cm$ to $2\; cm$ is

Four identical rods of same material are joined end to end to form a square. If the temperature difference between the ends of a diagonal is ${100^o}C$, then the temperature difference between the ends of other diagonal will be ........ $^oC$

A partition wall has two layers $A$ and $B$ in contact, each made of a different material. They have the same thickness but the thermal conductivity of layer $A$ is twice that of layer $B$. If the steady state temperature difference across the wall is $60K$, then the corresponding difference across the layer $A$ is ....... $K$

A slab consists of two parallel layers of two different materials of same thickness having thermal conductivities $K_1$ and $K_2$ . The equivalent conductivity of the combination is

Give definition, unit and dimensional formula of thermal conductivity.